Telephone-exchange system



H. HovLAND 1,708,946

TELEPHONE EXCHANGE SYSTEM April 16, 1929.

5 Sheets-Sheet l Filed June 15, 1927 April 16, y1929. H. HovLAND l 1,708,945

TELEPHONE EXCHANGE SYSTEM April 16, 1929. H. HovLA-ND 1,708,945

' r TELEPHONE EXCHANGE SYSTEM Fired June 1:5. 1927 5 sheets-sheet 5 v, E M M um n M 0 @n m 0 A IIL WuH V. v .Smm T /M Uhu 4,. k M F. H Sm ml Y H rT IIHL a um. vf. Sm, DU

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Patented Apr. 16, 1929 PAT ENT OFFICE.

lcfllENItY EOWLAND, OF FLUSHING, NEW YORK, ASSIGNOR TO BELL TELEPHONE LABO- .'itllrdi'Olll/JEES, lIilCORPOlEtATlSD, OF NEW YORK, lll'.

Y., A CORPORATION OF NEW YORK.

TELEPHONE-EXCHANGE SYSTEM;

Application 'filed June 13,

'.,lfhis invention relates to telephone exfhanggjc systems and particularly to improvex`- n rents in the establishment ot' inter-cinco co11- ncctions.

-icc-ordine to this invention, calls originatiu in satellites are first extended over trunk hunting switches to the central oliice where a selector switch is operated in accordance with the tir-st dig't. During the transmission of the lirst t' a sxcond trunk hunting switch in the satellite is caused to preselect an idle trunk leading to a local selector. If the call is a local one the central olhce selector sends bach a signal which brings about a release ot the central otlice trnnlrand the extension o t the subscribcnsline to the preselected local switch.

according to another feature of the invcn tion. an unstandard condition on a subscribcrs line causes the operation ot a signal at the central ollice to attract the attention of an attendant who is able to transfer the signal back to the satellite to one of the local selector switches therein. By transferring the signal to the satellite the central oliice trunk is freed.

Referring the drawing7 Figs. l, 2 and 3 when talaen in order illustrate the invention when embodied in a system employing f-iwitches of the step-bystep type. F ig. l shows a calling subscribers line, a line finder switch diagrainmatically and two single movement rotary trunk hunting switches located in the local or satellite exchange. In the upper portion of .F 2 is shown a re The lower portion ot this ligure shows a first selector switch also in the local exchange. Fig. 3 shows a 'lirst selector in full,` a second selector and connector diagrannnatically and a called subs .-iib ,as line in the main exchange.

ln the system shown a call originating in the satellite ottico first extended over the line linder F and the trunlr selector S to a trunk including the repeater It outgoing' to the central oillice. It the called line appears 'in the central oitlice the calling' subscriber transmits a number ot digits to operate the selectors S3 and S4 and the connector C to seize the called line. lhc impulses of these digits' are repeated by the repeater R located n t thc satellite oilice. lili, however, the called line appears in the satellite, the lirst digit transmitted will canse the selector switch S3 Vthe satellite 1927. Serial 110.198,45.

to step to a predetermined level of contacts which identify a local call. During the translnission of the lirst digit the repeater R functions in a manner to initiate the operation of the trunk hunting switch S1. `The switch S1 seizes an idle trunk leading to a local lselector switch S2 so that this switch will be ready for operation when it is needed. At the end of the first digit the switch S3 in the central oflice steps into the predetermined level whereupon battery connections to the tip and ring conductors of the trunk are reversed, reacting upon-the repeater R in such a way that the calling subscribers line is vdiscoimected from the switch S, the repeater' Rand the central oilice trunk and is switched tothe preselected local selector switch S2. '.lhc subscriber, continuing to transmit the remaining digits, sets the switch S2 and other switches, not shown, to extend his line to the called subscriherls line in the satellite. By this arrangement the changeover operation from central ol'Hce i is effected without danger of nnitilating impulses since the local trunk is preselected during the preliminary operation ot the central oliice selector.

l In the event a central ollice trunk is seized due to some unstandard condition or is otherwise held tor an unreasonable length of time, a permanentsignal is brought into play at the central oliice. The attendant in response to this signal short-circuits the tip and `ring conductors of the trunk leading hack to the satellite, causing the subscribers line to be switched from the central oliice trunk to a local selector where it operates another permanent signal to notify the attendant in the satellite.

A detailed. description will now be given, lirst assuiningl that the subscriber' of the line 100 in the satellite wishes to call another subscriber located in the same satellite. The subscriber oil the line 100, on initiating the call, causes the operation of a line linder F to search for the calling line. During the operation of the finder F ground potential is placed on the sleeve conductor 117 causing the operation of relay 101 in a circuit leading through the back contact of relay 102. Relay lOl closes a circuit for the stepping magnet G of the switch S. It switch S is standing on a busy trunk the sleeve brush lll is trunk to a local trunk in sive,

grounded and the circuit of stepping magnet 106 mayV be traced as y follows. Battery, through the winding and contact of the magnet, inner lower contact otrelay 101, normal Contact of relay 107 to the grounded brush 111. Thermagnet 106 interrupts its own cir- 101. During the stepping movement ot the v `106'fails`to energize.'

switch the relay 107 was short circuited and consequently ydid not operate. This relay ,operates now, however, in the circuit traced, but dueto its resistance the stepping magnet If the line finder F should find the calling liner100- before the switchS finds an idle trunk, the tip vand ring 'conductors of the subscribers line are extended through the front contacts ofrelay 101 and the back contacts'of -re'layf107- to the windings of relay 104. Relay M14-operates the relay 103 in an obvious circuitand relay 103 applies ground potential to the sleeve conductor 117. i

' When'thc idle trunk 118v is reached and the relaysV 101' and V107 operate, the subscribers line is extended over the back contacts of relay 200 tothe windings of the im- Y pulse relay 201 in the repeater. Relay 201 operates and closes a circuit from battery through the left winding of relay 300, lower back contact of relay 301 over the lower side of the trunk 209, contact of relay 207, right Winding of the electrically polarized relay 205, winding of relay 206, upper contact of relay 201 returning over the upper sideV of the trunk through the'back contact of relay 301, right Winding of relay 300, to ground at the normal contacts ofthe spring combination 302. Relays 300 and 206 operate inv this eircuit, but the direction of current flow is such that the polarized relay 205 does not operate. Y Relay 201 alsocloses an obvious circuit for slow release relay 204. Relay 204 at its right contact closes a circuit for the lett winding of relay 205, but as above noted, the relay 205 does not attract its armatures. Relay 204 also applies ground potential to the sleeve c0nductor-210. This grounded sleeve conductor is extended back to the brush 111, in-

ner lower Jfront contact of relay 107 to the sleeve conductor 117. This circuit is completed before ground is removed trom conductor 117 and thus a non-interrupted ground potential is maintained on the sleeve to prevent release.

The relay 300 at the central otlice in operating closes a circuit from battery through the winding of relay 303, winding of slow release relay 304, front contact ot relay 300, to ground at the back contact of relay 301. Re-

lays 303 and 301 operate. The apparatus is now ready to receive the ti rst digit.

The subscriber manipulates his transmitter to send the Erst digit and on the lirst interruption ot the line, relay 201 releases and closes a circuit trom ground through its lower back contact, 'front contact ot relay 204, winding oi the slow release relay 207 to battery. Relay 207 operates and closes a circuit from battery through the winding of slow release relay 202, contact of relay 205, lower 'front contact of relay 207, sleeve conductor 210 to ground at the right contact of relay 201. Relay 202 ccuuplctes a circuiti from ground through its right contact, conductor 227, brush 113, lower front contact o l' relay 107,1eft winding of relay 101 to battery. Relay 104 operates and closes an obvious circuit for relay 103 which connects its grounded armature to the conductor 117.

Relay 104 also initiates the operation of the trunk hunting switch S1 to preselect an idle local trunk. The stepping circuit for switch S1 leads from battery through the winding and contact ot stepping magnet 10S, right contact ot relay .101, lower normal contact of relay 105 to the brush 116. lt` the switch 1 1 stands on a busy trunk the brush 116 is grounded and the stepping magnet 108 operates to advance the brushes 114, 115 and 116 from position to position until an idle trunk 119 is reached. lVhen the idle trunk is found the switch stops.

Returning now to the point. where the subscriber commenced to operate his dial to transmit the first digit, relay 201 in releasing on the tirst interi-tuition also opens the eircuit of the impulse relay 300 at the central oiiice. Relay 300 completes a circuit from ground at the middle lower contact ot relay 301, conductor 311, back contact of relay 300, front contact ot relay 301, winding ot slow relay 30S and the vertical magnet 300 to battery. The magnet 309 steps the brushes 312 up to the first level of contacts. On the tirs-t step of the switch the primary ott-normal contact combination 310 is shifted and relay 305 operates in a circuit from battery through its winding, upper contacts 2110, contact ot' relay 30S to ground at the contact of relay 304. Relay 305 locks in a circuit from battery through its winding, contacts 310, contact of the magnet 306, outer contact of relay 305 to the grounded conductor 311.

On the next closure ot the lille, relay 201 in the repeater operates and recloses the circuit of relay 300. The circuit', is moditied, however, at the repeater so that it now extends over the upper conductor of the trunk 209, upper contact of relay 201, upper front contact of slow relay 207 to the lower side ot the trunk 209. This revised circuit excludes the windings o relays 205 and 206.

For each succeeding interruption, the relay 201 releases to in turn release the relay Cil when relay 207 releases.

300 which causes the selector to step :troni level to level until it reaches the predetermined levelcontaining the contacts 313, 314i and 315. lhese contacts are connected to battery and laroiuulas illustrated. llt the ond oli the liz-st series olf impulses the line is closed tor an interval and the slow relay 207 releases, opening' the circuit ol relay 202. 'lhe relay 300 remains operated in the circuit lirst 'traced and alter an interval relay 303 releases.

The rotary inagiiet 300 oit 'the selector E53 is next operated in a circuit from battery through its Winding@ Contact ol relay 305, normal Contact el relay 303 to ground at the Contact of relay 3011. The rotary niaginet 300 steps lnfushcs 312 to the lirst cet o1' terininals 313, 311 and 315 iu the pr uruiiueal level. Magnet 300 opens the circuit el relay 305 which releases and in turn opens the cir-- cuit o1 magnet- 306. litthe terminals on which the brushes 312 are now standing; are idle, no ground exists on test terminal 315 and a circuit is completed from battery through the winding el relay 305, upper contacts 310, contact of magnet 300, WindingI ot relay 301, upper contact 302 to ground at the contact olf relay 30e. l-lad the sleeve terminal 315 been grounded relay 301 would be shunted over a pathleading` through the louer bach coiitact ot'` the relay to the test brush. Relay 301 in operating disconnects the relay 300 and extends the tip and ring conductors through to the terminals 313 and 311. lt will be noted that the battery and ground connections applied to the terminals 313 and 3111 are opposite to those applied to the windings ot' relay 300. "This causes 4a reversal in the direction ot current flowing through the right wiiidinfT of relay 205 at the repeater. llc` cordingly, relay 205 operates and cou'lpletes a circuit from ground through its armature, lett iront contact oit' relay 202, conductor 211, brush 112, upper inner contact oil relay i", Windingr ol relay 102 to battery. It will be noted that the circuit of relay 202 is opened llel ay 202, however, is sutliciently slow in. releasingto maintain its arinatliu'es attracted until alter current re versal takes place over the trunk.

llelay 102 in operating closes a Circuit roin ground through its right contact, Winding oit relay 105, Contact and Winding oil magnet 103 to battery. llelay 105 operates in this circuit. Relay 102 circuit ol' relay 101 which releases and causes the release el relay 107. During' the time relay 202 is operated it maintains the relay 10d operated in the circuit traced through the lelt Winding` of the latter relay, Relay 10% holds the relay 103 to maintain ground potential on vthe sleeve conductor 11'?. llelay 10i in releasing' releases the relay 1041, but relay 103 remains operated to provide a local circuit for relay 102 and to maintain ground poat its left bach contact opens the tential on the conductor 117 until after the connection has been extended to the selector S2 in the satellite. llilli'th relay 101 released and relay 105 operated the tip and ring condoctors oit the calling line are extended throrurh the brushes 11a and 115i and the bach contacts o1E relay 212 to the windings or relay 213. 'lhe lett windiirgoit relay 213 is conhearted to batt-(ary and the right 'wiiuliiur is connected through normal contacts et the spi-ine; combination 211 to around. Relay 213 operates and completes a circuit troni battory through the winding' ol relay 215, windinc; oi slow release relay 210, liront contact of relay 213 to ground at the hachr contact oi,3 relay 212. llelay 210 operates and places grround potential on sleeve conductor 217. 'lliis sleeve circuit is extended back to the brush 110 and the lovrer lronteon tact oil relay 105 to the sleeve conductor 11i'. litter an interval relay 103 releases. V

'lhe disconnection of the subscribe1"s line 100 lroiu the repeater ll` results in the deener gisatiou oil" relays 201 and 2011.

allier an interval following1 the release of relay 300 the slow release relay 301 leenersizes. lilince the sleeve terminal 315 is blank in the predetermined level no substitute `rg'ir'ouiul potential is plared ontlie test brush betere/relay 301 releases. rllherelfore, when relay s.- releases the relay 301 also retracts its armatures. lhc release 1nae'net`307 is now enerui'fzeifl in a circuit from battery through its windings, closed contacts 310, bach contacts oil relays 3041- and 300 to ground at the hack Contact oit' relay 301. ll'lagnet 307 releases the suitch il in the well known nianner.

'lhe foregoing operations have all taken place in a very short interval oi? time. The subscriber next f noeeeds to transmit 'll i second series oil" impulses ropresentiiur the second digit oil the Wanted niuuber. .lures-poisse to the line interruptions relay 213 diufneiwizes and ene 'prizes and at each retrartion closes a circuit "lroin ground tlu'orugh the upper bach contact o relay 212, back contact et relay 213, trout contact oit relay 210, Winding ol' slow release relay 213, Windin ot the `vertical steppingmagnet 210 'to battery. lll'agnet 210 steps the brushes 220 troni one level to auother. llll'ith relay 213 operated and the vertical oll-norinal sp ina tion 221 shittcd a circuit completed roni battery through the winding ol relay closed contacts of the con'ibination 221, tron contact oli relay 213 to the grounded conductor 21'?. llelf locln n a circuit .troni battery throughi winding, upper contacts of combination 22 bach' contact olf the nuigignet 223, ri ight confact olf relay to ground at the u pyiier bach' contact oil relay 212.

y Altollowing` the second series oit in'ipuls-sos the sleuf' relay 213 releases :lad prepares a circuit lor the rotary magnet 223 to rotate the brushes in Search of an idle trunk. The circuit for the magnet 223 leads 'from battery through its winding, lett emita-ct of relay 222, nornial Contact oill re ay to the ,g unded conductor 217. N energizing opens'the locking Relay releases turn releasing the magnet 223. Iii the trunl; on which the brushes are new standing is busy relay is reoperatcd in a circuit -it'roni battery through its winding, oil-normal contacts 221, contact ot magnet conductor 221.., lower back contact et relay 212 to the grounded test brush 220. A parallel circuit also leads throughthe windingv et relay 212, normal conta ctsof the combination 2111- to the grounded sleeve conductor 217. `Relay 212, however, being shunted, ydoes not operate. llelay in operating recloses the operating circuitot magnet and the switch taires another .i cuit ol: relay rotary step. This operatizm continues until an ungrounded trunk is reached at which ti1ncfrelay222 remains dcenergir/ied to prevent further stepping of the switch. lclay 212 is also operated to extend the L and ring conductors through to the br ies 220 and to the switch beyond. The resistance of rclay 212 is such that the relay 222 does not 0perate in series therewith. Relay 21?) rcleaf-ses and after an interval. the slow relay 216 deenergizcs; Before relay 216 releases, however, the grounded sleeve conductor is extended back 'from the selector' beyond to Ymaintain ground potential on the conductor 217.

1n' similar manner the subscriber transn'iits the remaining impulses and suitable switches are positioned to extend his liner to the local called subscribers line.

After conversation has been completed the subscribers replace their receivers and ground potential is removed :from the sleeve conductor 217. Relay 212 thereupon releases and closes a circuit from battery through the winding ot rel-ease magnet 226, closed contacts 221, back contacts et' relays 216 and 213 to ground at the upper baclr contact of relay The magnet 226 vrestores the selector' switch S2 in the well known manner. The removal of ground potential from conductor 217 and consequently from conductor 117 releases the relay 102 which in turn releases the relay 105; The finder switch F is also restored in the usual manner.

Assume next that the subscriber of line 100 wishes to hold conversation with the subscriber out lineV located at the central oilice. Y The extension oit the connection to the central otiice takes place in the same manner thathereinbeliore iescribed. 1n response to the lirst digit the selector switch S3 adg varices its brushes 312 to some level other than the predetermined level above mentioned. For example, the brushes 312 may be positioned on the terminals of an idle trunk leading to the selector switch S. In this case as soon as the idle trunk is seized a ground potential is placed on the .sleeve brush to maintain the relay 301 operated following release oli rela-y 301. The holding circuit ot relay 301 may be traced from bat` tcry to the winding ot relay 2103, closed conta ts 310, contact of magnet 806, winding of relay 301, contacts 302. lower trout contact of' relay 301 to the grounded sleeve brush 312. Relay 305 does not operate in this circuit. Inasinuch as thc current flow over the trunk leading back to the satellite is not reversed in this case, polarized relay 205 does not operate. Consequently the subscribe1"s line 100 is not shifted as was the case when a local call was made. The subscriber continues to transmit impulses whereupon the selector S* and connector C are positioned in a .suitable manner to complete the extension of a connection through to the called line 318.

After conversation has taken place the subscribers release the connection in thc manner already described.

'llie permanent signal condition will next be described. Assume that the subscribers line 100 is closed, due to some unstandard condition or that a subscriber leaves his rcceiver ott the switchhook for an unreasonable lengt-h of time. This condition results in the seizure, in the manner fully described licreinbe'tore, of a trunk leading to central ollice. The relay 300 in operating causes the operation of relays 803 and 304. Relay 303 closes the circuit leading to a signal tevicc 320. 1f the condition prevails for a certain length of time the attendant at tbc central otlice responds to the signal 320 and inserts the plug 321 in the jack 322. This shortcircuits the relay 206 in the satellite and the relay releases. A circuit is now completed trom battery through the winding ot relay 203, outer le'tticontact'I ol" relay 204, contact of relay 206, lower back contact of relay 207 to the grounded conductor 210. Relay 203, which is slow to operate, locks to the conductor 210 and completes a circuit from ground through its inner' left contact, conductor 211. brush 112, contact of relay 107, winding of relay 102 to battery. Relay 203 at its outer left contact applies ground potential to the conductor 227 to operate the relay 104 which in turn operates relay 103. Relay 203 is made slow to operate to prevent its accidental operation due to momentary releases of relay 206 when current is reversed over the trunk 200. The circuitof relay 203 may also be closed momentarily on release of relay 207 and betore relay 206 operates. Relay 102 in operating switches the subscribens line through to the first selector' S2 as previously described and releases relays 101 and 107. Relay 103 holds ground potential on the sleeve 117 until relay 216 in the first selector operates to ground this conductor. The relay with fsaid selectors, lines appearing in said o'ice, a .second office having selector switches therein, a trunk interconnecting said oflices,

means for extending a connection from one of said lines over said trunk to a selector switch in the second oce, yineens controlled from the lseconol olice for releasing the trunk and the l6 v Y 1,708,946

extended connect-ion and for extending said line to one of the selector switches in the first oliae, and means responsive to such extension 10 for actuating the signal in said iirst office.

In witness whereof, I hereunto subscribe my nume this 10th day of June, A. D. 1927.

HENRY HOVLAND. 

